La. Paquette et al., CONCISE SYNTHESIS OF CIS-THEASPIRONES AND TRANS-THEASPIRONES VIA OXONIUM ION-INITIATED PINACOL RING EXPANSION, Journal of organic chemistry, 61(3), 1996, pp. 1119-1121
The odoriferous principle of black tea has been produced from 2,2-dime
thylcyclopentanone. The reaction sequence begins with 1,2-addition of
5-lithio-2-methyl-2,3-dihydrofuran to this ketone and immediate acid-c
atalyzed ring expansion of the resulting carbinols to a separable pair
of spiro ethers. Individual conversion of these diastereomers to a,P-
unsaturated ketones is followed by tandem condensation with the methyl
lithium-lithium bromide complex and oxidation with pyridinium chloroch
romate.